Persulfate is a strong oxidant that has been widely used for initiating emulsion polymerization reactions, clarifying swimming pools, hair bleaching, micro-etching of copper printed circuit boards, and TOC analysis. Among all the persulfate salts typically manufactured (sodium, potassium, and ammonium salts), the sodium form is the most commonly used for environmental applications in the last few years. Sodium persulfate has the potential to in-situ destruct chlorinated and non-chlorinated organic compounds commonly encountered in contaminated soil and groundwater. Other peroxyanions, such as peroxydiphosphate, persilicate, and perborate are also used in bleaching applications.
The persulfate anion (S2O82−) and other peroxygenated anions such as peroxydiphosphate, persilicate, etc. can be activated by various methods (heating, UV, transition metal catalysts) to give highly oxidizing radicals. For persulfate, the formed SO4− radical has found use in disinfecting water and in removing organic contaminants. Readily available sources of persulfate include Na2S2O8, (NH4)2S2O8, K2S2O8, etc. These compounds are very soluble in water, and thus when applied to treat a water sample, the radical action is spread over the water's entire volume.
Therefore, in order to treat a large water body, fairly high concentrations of persulfate are required. It has not been possible, to the best of our knowledge, to confine the action of peroxygenated radicals to a desired limited space. Therefore, applications which would benefit from local oxidation, such as filtrations, coatings, etc. (as seen for TiO2 photooxidation systems) have not been possible for peroxygenated anions, even though these oxidants have a distinct advantage over other materials in terms of easy activation.
Accordingly it is desirable to provide a system and method to confine the action of reactive radicals to a limited space, which would enable the fabrication of an effective filter system with oxidizing power for water disinfection and air purification.